But I guess one night I had a few
Huh, one night I had a few
Yeah, this little chick that caught my eye
I told her "hurry up, meet me at the room"
And no, I didn't have a contraceptive
What my common sense neglected

from T.I. (Ft. B.o.B, Kendrick Lamar & Kris Stephens) – Memories Back Then Lyrics on Rap Genius


B.o.B was drunk one night, and, neglecting his common sense, slept with this girl (without any condom) who wasn’t the girl he was seeing.
Alcohol can have that effect.

The “without any contraceptive” points out why B.o.B. immediately thought the child was his, a few lines later. And immediately told his girlfriend that he cheated and made another girl pregnant by doing that.

(later seems that the kid wasn’t his though, but there was a big chance, since they did it without protection)

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